This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Flow-mediated dilation (FMD) of the brachial artery using high-resolution ultrasound is a well accepted non-invasive bioassay for in vivo endothelium-generated nitric oxide (NO) in humans. NO has been characterized as a potent vasodilator, but NO also has a considerable role in maintaining healthy endothelium and inhibiting key steps in the development, progression, and clinical manifestations of atherosclerosis. Because the postprandial state may be critical in the development of atherosclerosis, and because diets high in cereal fiber have been linked to reduced risk of cardiovascular disease, we hypothesize that a high-carbohydrate, high-fiber meal would acutely improve FMD. By contrast, we hypothesize that a low-carbohydrate meal will impair FMD, and that a high-carbohydrate, low-fiber meal will have no effect on FMD. We also hypothesize that the addition of a high-fiber breakfast cereal to the low-carbohydrate meal will attenuate the impairment of FMD observed after the low-carbohydrate meal. Brachial artery flow-mediated dilation (FMD) will be assessed before and at 2 h and 4 h after each of four breakfast meals (high-carbohydrate, high-fiber;high-carbohydrate, low-fiber;low-carbohydrate, low-fiber;low-carbohydrate, high-fiber) using high-resolution ultrasound and edge-detection software in 12 participants ages 8-17 who are overweight or at-risk for overweight, 12 participants ages 18-64, and 12 participants ages 65 and older. Analysis of variance with repeated measures will be used to assess differences in FMD in response to the meal challenges.